i am trying to run a periodic flow of a part of a pipe. I chose the eights part of a pipe and set up the inlet and outlet as translational periodic and the long surfaces as rotational periodic and the curved surface as wall. After i defined the mass flow rate in translational direction and solved the flow and turbulence with the k-w SST model. It worked quite well and the pressure drop in the pipe part is nearly the same as calculated in the empirical model of Pethukov (<1% for Re=37000).

So after solving the flow and turbulence i turned off solution for flow and turbulence and turned on energy for the heat transfer solution.